Treatment of solid materials



United States Patent Inventors Robert A. Gladstone 9 Glen Road, NewtonCentre, Mass. 02159, and Anthony Kettaneh, 77 Browne St., Brookline,Mass. 02146 Appl. No. 684,044

Filed Nov. 17, 1967 Patented Nov. 10, 1970 TREATMENT OF SOLID MATERIALS18 Claims, 8 Drawing Figs.

US. Cl 299/14; 175/16; 219/121; 241/1; 125/1 Int. Cl E2lc 37/16 Field ofSearch 299/14;

175/11-16(Inclusive);331/94.5;241/1;125/ (Inclusive) (Examiner); 219/12(Laser) [56] References Cited UNITED STATES PATENTS 2,859,952 11/1958LaTour et al. 299/14 3,219,280 11/1965 Seldenrath eta]. 299/14X3,265,855 8/1966 Norton 331/94.5X 3,321,248 5/1967 Williamson et a].299/1 Primary Examiner-Ernest R. Purser Attorney-Irving Kayton ABSTRACT:A method for weakening a solid material, such as a rock formation, bydirecting a beam of electromagnetic energy generated, for example, froma laser source toward the material to cause it to impinge thereon and topenetrate beneath the surface thereof. The energy is preferably in theform of a collimated beam having a wavelength selected so that theenergy is substantially absorbed by the material.

LOAD (kg) Sheet "FIGLI i I i i i i 1' 1 INVENIORJY: v.

mm RLA GLADSTONE ANTHONY K'EHANEH TREATMENT OF SOLID MATERIALS Thisinvention relates generally to methods for treating solid materials and,more particularly, to methods for treating hard rock formations or othersolid mineral, or minerallike, materials with electromagnetic energy, asfrom a laser beam, so as to weaken their mechanical structure andthereby make easier the excavation of, or tunneling through, suchformations.

ln earth excavation processes as, for example, underground tunneling orwell drilling, the presence of hard rock minerals in the form ofgranite, marble, gneiss, schist, and the like, increases the cost andreduces the efficiency of such operations by increasing the timerequired for such excavation and by causing excessive wear or damage tomachine tools used therein. It is desirable, therefore, to deviseeconomic and efficient methods of treatment for weakening the structureof such hard rock formations prior to the application of excavationmachinery thereto. By causing fractures or'otherwise weakening thematerial its strength can be reduced to a point where such machinery canmore easily and quickly remove the treated debris with less expenditureofmechanical energy and less wear on or damage to the removal machinery.

Conventional excavation methods which involve drilling,

charging and blasting the hard rock formation, and finally such methodsmust be performed in a sequentially repetitive manner by many highlypaid workers requiring different skills and training. The inconvenienceand costs of such processes make it highly desirable that otheroperating procedures be devised to provide faster, safer, less expensiveand more effieient excavation systems.

Other more sophisticated methods have been suggested and used to cause adeterioration of the mechanical strength ofthe materials. Suchprocesses, for example, involve the direct application ofheat to thematerial, the heat being generated con ventionally by a suitable flamesource, such as an oxygen-gas torch. In the use of such a method,further improvement in the weakening operation has sometimes beenobtained by quenching the material with water or other suitable coolingliquids immediately or at least shortly after the firing operation. Thethermally induced shocks and resulting stress distribution that occurgenerally weaken the structure of a rock sive amount of time may berequired to generate sufficient surface heat to cause an effectivefracturing or weakening of the rock material.

Other methods which have been tried, at least experimentally, haveutilized means for generating electric or magnetic shocks or forproducing sonic vibrations in an effort to cause a fracturing of thematerial. Such methods generally have not proved to be sufficientlyeffective or commercially feasible at least at the present time. V

This invention utilizes a method which overcomes the deliciencies ot'the above methods and, more particularly, greatly reduces the timepreviously needed to cause a sufficiently effective weakening of thehard rock structures involved. The invention additionally appears toshow promise in effectively reducing the overall operating costs of theexcavating or tunneling process. In the method of the invention anelectromagnetic energy source, such as a laser device, is used forgenerating an energy beam which is directed toward at least one ex posedsurface of a rock formation which is to be treated. Heretofore, whenlaser beams have been applied to solid materials,'such as metals, theyhave been known to penetrate such materials and to form well-definedholes therein. However, when applied to rock materials, no appreciableweakening effects have been noticed. In the latter cases, the beams insome cases have appeared to melt or at least partially vaporized thematerial in localized areas, thereby causing the formation of vitreousor glasslike zones around the edges of such localized areas ofpenetration. Such zones have tended to achieve a greater hardness thanthat of the original material and it was believed that their presencemay have tended to enhance the strength of the materials rather than toweaken it. In some cases, application of a laser beam has even appearedto cause previously existent fissures within such materials to becomesealed by fusion and thereby the material had also seemed to be furtherstrengthened. Moreover, a substantial amount of the beam energy hasappeared to be wasted because it had been reflected and therebyreradiated from the material before it had served any useful purpose.

The lack of success in using laser beams for weakening or fracturingrock materials has tended to prevent those in the art from furtherinvestigating the possibility that electromagnetic energy would proveuseful in the field of hard rock excavation. This invention, however,provides a successful method for utilizing electromagnetic energy, asobtained from a laser, to weaken rock formations by using anelectromagnetic energy beam having a wavelength selected so that theenergy is substantially highly absorbed by the-rock material at or nearthe surface thereof. It is found that the absorption of such energyhaving a frequency within an appropriately selected frequency rangecauses a reduction in the tensile strength of the material and therebyproduces an effective overall degradation of its mechanical strength.Contrary to the prior art, but in accordance with the principles of theinvention,a nonconverg ing beam, preferably eollimated, may he used toachieve this result.

A specific type of laser device that has proved to be effective forproviding such electromagnetic energy is a moleculargas laser utilizinga combination of selected gas molecules as the lasing medium. Selectedareas on an exposed surface of the rock structure are irradiated withthe laser beam from such device for appropriately designated timeperiods. In one preferred embodiment, for example, the laser beam whichhas been found useful in treating marble or granite structures has afrequency in the far infrared region of the frequency spectrum.

Appropriate tests show that the effective depth of penetration of such alaser beam may be several inches. The thermal stresses which areproduced because of the intense heat generated at or near the surface ofthe material by absorption of the laser beam energy cause the formationof a plurality of primary cracks or fissures within the materialaccompanied by an additional plurality of side cracks. As discussed inmore detail below, the treatment of sample specimens of such materialsshow considerable reduction in the value of a load, applied in tension,that is required to deflect the material to its failure, or breaking,point as well as a considerable increase in the crack area which isformed.

In some applications a preferred embodiment of the invention utilizes asystem in which electromagnetic energy from a laser is in the form of acollimated beam in which the energy rays making up the beam are allessentially parallel. Such a system provides advantages in applicationswhere laser ener gy, for example, is generated at a remote location fromthe rock formation and such collimated beam energy can be easilytransmitted from thesource to the rock surface under treatment by anappropriate mirror transmission system. In other applications it may bedesirable to produce a high concentration of energy at a small localizedsurface area in-which case a noncollimated, converging beam of energymay be utilized.

The invention can be described most easily with the help of theaccompanying drawings wherein:

FIG. 1 shows a partially pictorial, partially diagrammaticrepresentation of a simple version of a proposed configuration whichutilizes the method of the invention;

, prising a plurality of substantially concentric rings 17 whichirradiated in a pattern of concentric circular areas in a FIG. 2 shows adiagrammatic representation of one form of a laser beam irradiationpattern useful in practicing the method of the invention;

FIG. 3 shows a representative sample of a block of granite used fortesting the effects of laser beam irradiation applied in accordance withthe invention;

FIG. 4 shows another representative sample of a material used in testingthe effects of the use of the method of the invention;

FIG. 5 shows a graph of representative load-deflection curves comparingthe weakening effect of untreated materials and materials treated inaccordance with the method of the invention;

FIG. 6 shows a graph of representative curves showing incremental crackareas produced as a function of exposure time for such treated anduntreated materials;

FIG. 7 shows a partially pictorial, partially diagrammaticrepresentation of an alternative configuration of the invention whichutilizes a converging beam of electromagnetic energy; and

FIG. 8 shows a partially pictorial, partially diagrammaticrepresentation of a proposed configuration of the invention using aremotely located electromagnetic energy generator.

With reference to FIG. I, it is desired, for example, to excavate a rockformation It) so as to form a tunnel having an opening ll therein. Inthe figure a laser device [2 is mounted on a suitable structure [3 on anappropriate pivotal mount 14 which allows the beam I5 from laser device12 to be controllably directed toward rock structure 10. Structure 13may be used to house suitable control and power supply circuitry as wellas monitoring or other peripheral equipment. Any suitable mounting meanswell known to those skilled in the art can be used and, consequently,such a structure is shown only schematically and the details thereof arenot further discussed here. The laser beam 15 may be controllablymaneuvered to impinge generally upon the front exposed surface 16 ofrock formation 10 within opening 11 in some suitable selected pattern.Such a pattern may be of the form shown in FIG. 2 comtend to cover anappropriate portion of the overall area of the front surface I6.

Laser device I2 is a device presently well known to those in the art forproducing a beam of energy through a process generally referred to asstimulated emission. In one particular embodiment, for example, althoughnot necessarily limited thereto, such laser device may be of themolecular-gas type which utilizes as a lasing medium a combination ofgaseous materials in which a required population inversion of themolecules within such medium occurs. One particularly useful gaseouscombination includes carbon dioxide, nitrogen and helium which producesan output radiation beam in the far infrared region of the frequencyspectrum, such beam having a wavelength of approximately l0.6 microns.Molecular-gas 5 lasers of this type are known, at the present time atleast, to produce higher efficiencies than many other presently knownlaser devices which, for example, may utilize a combination of noblegases or which may utilize solid state mediums, such as ruby orsemiconductor materials,

In the particular embodiment discussed herein, the laser is arranged toproduce an appropriate output beam of electromagnetic energy which, whenapplied to the exposed surface of the rock formation, produces asubstantial weakening of the rock structure. In such a laser device, forexample, the output beam is arranged'in the form ofa collimated beam ofenergy, that is, a beam in which the rays are all substantiallyparallel, such as is shown by collimated laser beam 15 of FIG. 1.Typical effects of such beam on the strength of the rock material beingirradiated can be generally discussed with reference to FIG. 3. In suchFIG. the rock formation is conveniently represented by a sample block I8ofgranite having a front surface area of approximately 1 foot square anda depth of approximately 6 inches. The front surface I9 of block [8 iskit . manner similar to that shown in FIG. 2. Tests on the effectivenessof laser beam irradiation on such a block show that the weakeningeffects of the beam occur both near the surface and well into theinterior of the block up to depths of 4 to 5 inches below the surface onwhich the laser beam is impinging. Maximum weakening effects appear tooccur generally in those interior volumes of the block which areessentially directly behind the areas 20 which are irradiated, theeffects of fracturing of the block generally being less in thoseinterior volumes not in line with the radiated areas. Such effectiveweakening was achieved in one instance by utilizing laser beamirradiation over a time period of approximately 30 seconds foreach 4square centimeters of surface covered. For a similar size block ofmarble, weakening effects were found to exist up to depths ofapproximately 3 to 4 inches. Thus, the severity of damage to the rockformation appears to be somewhat dependent upon the type of materialbeing irradiated.

The weakening effects may be demonstrated in more detail ifconsideration is given to the curves shown in FIGS. 5 and 6. Such curvesare representative of the weakening effects noted with respect to theapplication of a collimated laser beam having a wavelength substantiallyequal to 10.6 microns to typical samples of material fabricated in theform of rectangular beams which are substantially 1 foot in length and 1square inch in cross section. One such sample 2] is illustrated, forexample, in FIG. 4. The results of tests performed upon samples ofmarblematerial are discussed with reference to FIGS. 5 and 6. Similar resultshave been obtained on samples of other rock materials. A collimatedlaser beam, as from laser device 12, is directed toward the centralportion 22 of various samples 21 for varying amounts of time. Eachsample is thereupon subjected to a load which produces a tensile stresson the irradiated surface of the sample so as to deflect the sample.Curves 23 and 24 showing the relationship between the applied load andthe deflection ofthe sample are shown in FIG. 5 for irradiation times of3-5 seconds and 10 seconds, respectively. Such curves can be compared toa similar curve 25 for an untreated sample specimen. The area under eachof the curves represents the input energy requirement and is much lessfor the treated samples shown by curves 23 and 24 than for the untreatedsample shown by curve 25. Moreover, the maximum load required forfailure is reduced considerably even for such relatively low exposuretimes.

Further evidence of structural weakening is shown in FIG. 6

where appropriate micrographs of the specimen were used to.

measure the crack area produced by electromagnetic energy irradiationfor varying exposure times as compared to the original crack areaexisting for the untreated condition of the sample.

The increase in effective crack area and the decrease in input energyrequirements to produce failure indicate the use fulness of the methodof the invention for weakening hard rock formations. Once suchformations have been effectively weakened, the excavation process canproceed more quickly and easily since the weakened material can be thenremoved with far less wear, or possible damage, to the removalmachincry.

FIG. 7 shows an alternative embodiment of the invention in which anoncollimated beam of energy is utilized. In such embodiment thenoncollimated beam having a wavelength such that the energy will beabsorbed by the material under treatment is in the form of a convergingbeam 26 which is formed by focusing a parallel or collimated beam 27from laser device 12 by a suitable lens 28. The beam is caused thereuponto focus at a localized point 29 located in a plane essentiallycorresponding to the plane of the surface 16 of rock formation I0. Theuse of a noncollimated, converging beam provides similar weakeningeffects on the rock formation in the same manner described above withreference to collimated beam 15 of FIG. I. In the case of the convergingbeam, graphical results similarto those 'shown in FIG. 5 and FIG. 6 areobtained in which the area under the load-deflection curve, and hence,

the energy requirements are reduced considerably, the maximum loadrequired for failure is reduced over that required for an untreated rocksample and the effective crack area is increased upon treatment with aconverging beam.

The advantages of utilizing either a collimated or a converging beamsystem may depend upon the particular applications involved. Forexample, while the converging beam system allows a higher concentrationof energy at a relatively small localized area, it requires the laser tobe located substantially at a specified distance from the rock formationsurface so that the focal point of convergence lies, at leastapproximately, in the appropriate plane of the exposed surface of theformation. If a collimated beam is used, the location of the laserbecomes much less critical since substantially little or no energy islost in the transmission from the electromagnetic laser energy source tothe rock formation and the diameter of the collimated beam remainssubstantially constant for relatively long distances.

The collimated beam system may also find advantageous application insituations illustrated in FIG. 8. In such a system the electromagneticenergy source, such as laser 12, may be located at a position 30 abovethe ground over which the excavation is taking place. The outputcollimated beam [5 from laser source 12 may be directed toward asuitable reflective surface, such as a mirror 31, which will thereupondirect the energy downward through an appropriate opening 32 in theground toward a second reflective surface, suchas mirror 33, locatedunderground. Mirror 33 then directs the beam toward surface 16 ofunderground rock formation 10. Mirror 33 may be pivotally mounted sothat the position of the mirror can be varied and beam 15, as reflectedtherefrom, can be controllably directed to impinge on any portion of theoverall exposed surface 16 of rock formation 10. In this way the energysource can beremotely located to provide greater convenience inoperation and to prevent any damage to the source, which damage may bemore likely to occur if the source is locatedunderground during theexcavation operation. Since there is substantially little or no energyloss or increase in beam diameter in the transmission of energy beamfrom laser source l2 to surface 16, such an arrangement may prove highlyadvantageous in many applications.

In providing ancffective weakening in the structure of the materialsbeing excavated, whether by using a collimated or noncollimated beam.the wavelength (or, correspondingly, the frequency) of theelectromagnetic energy used must be selected to provide a high degree ofenergy absorption by the material. An appropriate irradiation time andpattern can then be selected to cause the beam to impinge upon portionsof an exposed surface of the material which is to be weakened. Forcertain rock formations, such as marble, granite, gneiss and schist, andthe like, the energy has been found preferably to have a frequency inthe far infrared region of the frequency spectrum and can be applied ina preselected pattern for time periods over a range as low as from oneor a few seconds to approximately halfa minute or more.

We claim:

1. A method for weakening a rock formation comprising the steps of:

generating a collimated beam of electromagnetic energy by a laser devicehaving a wavelength such that the energy from said beam is capable ofbeing substantially absorbed by said formation; and

directing said beam towards said formation to cause said beam to impingethereon and to penetrate beneath the surface thereof.

2. A method for weakening a rock formation in accordance with claim Iwherein said electromagnetic energy has a wave length in the farinfrared region ofthe frequency spectrum.

3. A method for weakening a rock formation in accordance with claim 1,wherein said electromagnetic energy has a wavelength of approximatelyl0.6 microns.

4. A method for weakening a rock formation in accordance with claim lwherein said laser beam is in the form of a nonconverging collimatedbeam of ener y.

5. A method for weakening a roe formation in accordance with claim 3wherein said laser beam is generated at a location remote from said rockformation and further including the step of transmitting said collimatedbeam from said remote location to said rock formation.

6. A method for weakening a rock formation in accordance with claim 1wherein said laser beam is in the form of a converging beam of energy,the focal point of said converging beam being located approximately atsaid surface of said rock formation.

'7. A method for weakening a rock formation comprising the steps of:

generating a laser beam of electromagnetic energy having a wavelength inthe infrared region of the frequency spectrum; and

directing said beam toward at least one surface of said rock formationto cause said beam to impinge thereon and'to penetrate beneath thesurface thereof so as to reduce the tensile strength of said rockformation.

8. A method for weakening a rock formation in accordance with claim 7wherein said beam is caused to impinge on the surface of said rockformation for a preselected time period sufficient to cause a weakeningof said formation.

9. A method for weakening a rock formation in accordance with claim 7wherein said beam is caused to impinge on the surface of said rockformation in accordance with a preselected pattern.

10. A method of claim 7 wherein said beam is nonconverging.

ll. The method of claim 7 wherein said beam is converging.

12. A method for excavating a rock formation comprising the steps of:

generating a laser beam of electromagnetic energy having a wavelength inthe infrared region of the frequency spec-v trum; directing said beamtoward at least one'surface of said rock formation to cause said beam toimpinge thereon and to penetrate beneath the surface thereof so as toweaken the mechanical structure of said rock formation; and removingsaid weakened rock formation.

[3. A method for controllably fracturing an object of solid materialcomprising the steps of generating a laser beam having a wavelength suchthat the energy from said beam is susceptible of being substantiallyabsorbed by the particular material ofsaid object; directing said beamtoward said object to cause said beam to impinge thereon and topenetrate beneath a surface thereof whereby mechanical weakening of saidmaterial at and beneath said surface is achieved.

14. The material fracturing method in claim 13 wherein said laser beamhas a wavelength of approximately 10.6 microns.

, 15. The material fracturing method recited in claim 13 wherein theduration of time said beam is directed toward any part of said object isa function of the dimension of said object along the direction. of saidbeam and is longer as said dimension is greater.

16. The material fracturing method in claim 13 wherein said laser beamis collimated.

17. The material fracturing method in claim 13 including the step ofmoving said beam over said surface of said object in accordance with apreselected pattern to cause fracturing of said object along the path ofsaid beam's movement defined by said pattern.

18. The material fracturing method ofclaim 17 wherein said pattern iscurvilinear;

